Non-dispersive infra-red (NDIR) gas sensors take advantage of selective absorption of radiant energy by specific gases. Analysis of absorption of specific wavelength(s) by a fluid sample provides an indication of the concentration of one or more gases of interest in the sample. The reliability of this process is dependent on the removal or exclusion of water vapor from the sample, including prevention of condensation of water vapor in the sensor.
It has been known to use configurations formed of compressed steel balls in explosion proof gas detectors. The compressed steel balls prevent any gas ignition in the chamber from propagating out to an explosive environment. These types of configurations would inherently provide some dehumidification of gas entering the detector. The dehumidification performance of such a configuration is generally poor since ambient air velocities can provide an unrestricted supply of water vapor to this type of configuration. In these known detectors, gas passes through the configuration of steel balls and into a sensing chamber without first passing through a filter.
One alternate known solution to the problem has been to incorporate an electric heater in the sensor to eliminate condensation of water vapor in the sample. In addition to requiring inclusion of a heater in the sensor, heaters require electrical energy when operating. Heater electrical requirements can become a major problem in systems that include large numbers of dispersed sensors that are powered off of common power and data lines. The power requirements of heaters are also a problem in portable or wearable sensors.
There thus continues to be a need for water vapor excluding, condensation minimizing, sensors that do not require heaters. Preferably, such sensors could be implemented without substantially increasing manufacturing expense or complexity. It would also be preferable if such implementations were compatible with the low weight, low power, low cost requirements of wearable sensors.